The known RTM (Resin Transfer Molding) process employs molds made of steel for withstanding the high pressures, even higher than 15 bar, needed for the injection of the resin.
The shaping of the fiber layers and their subsequent deposition into the molds can be automated, thus making more repeatable and economic the parts produced with this process, however the molds of the RTM process are heavy, expensive and bulky. Moreover, the metal molds need a complex design which must take their thermal expansion into account during the curing cycle of the resin, to avoid the molded product being clogged inside a mold.
The RTM-Light process, in which a semirigid mold is arranged on a rigid mold, is known for overcoming these technical problems. The resin is injected at a pressure lower than 1 bar and air (0.5 bar) is sucked from a central low point for favoring the flowing of the resin. The joining between the two molds is obtained by creating vacuum (0.1 bar) along the edges of the two molds. This process, though it is simple to be carried out with light and economic devices, does not allow to manufacture products with the same speed and the same quality of the RTM process, since the injection pressure is relatively low and the side of the product facing the semirigid mold has a rough finish. Furthermore, the low pressure employed in the RTM-Light process does not ensure the correct and complete impregnation of the dry fibers, thus causing the manufacture of low quality components.
EP 1721719 and FR 2864801 disclose RTM processes in which the molds are made of composite materials. In particular, the molds disclosed in FR 2864801 are in turn made by means of a RTM process in which the resin is injected only after the fibers have been arranged between a mold made of a composite material and a master or a template. These known molds are relatively expensive due to the RTM process employed for their manufacturing and to the need of arranging a template between a first mold which is already ready and a second mold during the manufacturing of the latter. The known molds made of a composite material further require complex supporting structures and/or must be relatively thick, thus expensive, for withstanding the pressures of the RTM process.